Oxirane production using peroxidized compound

ABSTRACT

Process for manufacturing oxirane by reaction of an olefin with a peroxide compound in the presence of a catalyst and a solvent in at least two reactors arranged in series, each of which contains a portion of catalyst, according to which the peroxide compound is introduced only into the first reactor, the subsequent reactor(s) not being fed with fresh peroxide compound, but only with the peroxide compound which is present in the medium obtained from the preceding reactor and which was not consumed in this preceding reactor.

[0001] The present invention relates to a process for manufacturingoxirane by reaction between an olefin and a peroxide compound in thepresence of a catalyst and a solvent. In particular, the inventionrelates to the manufacture of propylene oxide (or epichlorohydrin) byepoxidation of propylene (or allyl chloride) using hydrogen peroxide inthe presence of a catalyst containing TS-1.

[0002] It is known practice to manufacture propylene oxide by reactionbetween propylene and hydrogen peroxide in the presence of TS-1. Forexample, in patent U.S. Pat. No. 5,849,937, such a process is performedin several reactors arranged in series. In this known process, eachreactor of the series is fed with fresh hydrogen peroxide.

[0003] The Applicant has found that when each reactor is fed with freshhydrogen peroxide, it is impossible to convert the entire amount ofhydrogen peroxide used without substantial formation of by-products andthus impossible to have an optimum yield.

[0004] The present invention overcomes this drawback by providing anovel process which makes it possible to convert 100% of the amount ofhydrogen peroxide introduced, with a low formation of by-products andwithout, however, reducing the reaction rate.

[0005] To this end, the invention relates to a process for manufacturingoxirane by reaction of an olefin with a peroxide compound in thepresence of a catalyst and a solvent in at least two reactors arrangedin series, each of which contains a portion of catalyst, according towhich a first portion of the olefin, the solvent and all of the peroxidecompound are introduced into a first reactor, an epoxidation of thefirst portion of the olefin is carried out therein in order to form afirst portion of the oxirane, a medium comprising the first portion ofthe oxirane formed, the solvent, the unconsumed peroxide compound andpossibly the unconverted olefin is removed from this reactor, the mediumand another portion of the olefin are introduced into a subsequentreactor, an epoxidation of the other portion of the olefin is carriedout therein using the unconsumed peroxide compound obtained from thefirst reactor, in order to form another portion of the oxirane, and theother portion of the oxirane thus formed is collected.

[0006] One of the essential characteristics of the present inventionlies in the fact that the peroxide compound is only introduced into thefirst reactor. The subsequent reactor(s) is (are) thus not fed withfresh peroxide compound, but only with the peroxide compound which ispresent in the medium obtained from the preceding reactor and which hasnot been consumed in this preceding reactor. In general, water is alsointroduced with the peroxide compound into the first reactor. The factthat no peroxide compound is added to the subsequent reactor(s) makes itpossible to consume 100% of the total amount of peroxide compound usedwithout, however, reducing the reaction rate when compared with aprocess using the same total amount of peroxide compound, but in whicheach reactor is fed with fresh peroxide compound.

[0007] In the process according to the invention, a plant comprising atleast two epoxidation reactors arranged in series and connected togetheris used. Each reactor is fed with olefin. The peroxide compound and thesolvent are only introduced into the first reactor. Each reactorcontains a portion of the catalyst which does not leave that reactor.When the catalyst is present in the form of a fixed bed, it is generallynot necessary to take precautions to keep the catalyst in the reactor.Alternatively, the catalyst may be present in the form of particles, atleast some of which are in a form fluidized by a liquid stream or bymechanical stirring or by a gas. When a liquid stream is used, it isrecommended to include a fall-out zone above the fluid bed to stop thecatalyst particles which are in motion and/or to include a filter at thereactor outlet.

[0008] Needless to say, the plant may comprise more than two reactorsconnected in series. In this case, the first reactor of the series isfed with the olefin, the peroxide compound and the solvent and eachsubsequent reactor is fed with the olefin and the medium obtained fromthe preceding reactor of the series. Preferably, 3 reactors in seriesare used.

[0009] In the process according to the invention, at least 50% of thetotal amount of peroxide compound used in the first reactor is generallyconsumed in the first reactor. The best yields are obtained when atleast 70% are consumed in the first reactor. Usually, not more than 99%are consumed in the first reactor, and preferably not more than 85%. Theremainder is consumed in the subsequent reactor(s).

[0010] In the process according to the invention, reactors of identicalsize are preferably used. This makes it possible to interchange thefunction of the reactors when the deactivated catalyst in one reactor isreplaced with fresh or regenerated catalyst without disrupting thefunctioning of the plant (so-called “carousel” functioning).

[0011] A first embodiment of the process according to the inventionconsists in using the catalyst in the form of particles, at least someof which are in fluidized form, as disclosed in the Applicant's patentapplication filed on the same day as the present patent application andentitled “Process for manufacturing oxirane in the presence of acatalyst in the form of particles” (the content of which is incorporatedby reference). In this case, it is recommended to include a filterthrough which the medium leaving the first reactor passes before beingintroduced into the subsequent reactor. This embodiment makes itpossible to obtain a homogeneous dispersion of the catalyst in theepoxidation reaction medium, good heat exchange and thus easy control ofthe reaction temperature.

[0012] In a second embodiment of the process according to the invention,the medium entering the subsequent reactor is first subjected to adepressurization before being introduced into the subsequent reactor.This embodiment is particularly suitable when the epoxidation is carriedout under pressure or in the presence of a gaseous compound. Thisgaseous compound may be the olefin itself (for example propylene) or aninert gas which is introduced into the epoxidation reaction medium toallow the oxirane to be entrained and removed from the reactor, asdisclosed in patent application WO 99/48883 by the Applicant.

[0013] In a third embodiment of the process according to the invention,the medium entering the subsequent reactor is first subjected to atreatment to separate out the oxirane formed before being introducedinto the subsequent reactor. The aim of this embodiment is to separatethe oxirane from the epoxidation reaction medium as quickly as possibleafter it is formed in order to prevent the formation of by-products byhydrolysis or alcoholysis (methanolysis when methanol is used assolvent) of the oxirane formed. This embodiment thus has the advantageof leading to a high selectivity. The separation treatment is preferablya distillation, as disclosed in the Applicant's patent application filedon the same day as the present patent application and entitled “Processfor manufacturing oxirane comprising the separation of the oxirane fromthe reaction medium” (the content of which is incorporated byreference).

[0014] One preferred embodiment of the process according to theinvention is represented schematically in FIG. 1. In this preferredembodiment, the first reactor 1 contains a portion of the catalyst,preferably as a fluid bed 2. The reactor 1 is fed with a first portionof the olefin via pipe 3 and then via pipe 4, with peroxide compound viapipe 5 and then via pipe 4, and with solvent via pipe 4 obtained fromanother part of the plant which is described later. In the firstreactor, the first portion of the olefin reacts with the peroxidecompound in the presence of the catalyst to form a first portion of theoxirane. The medium leaving reactor 1 via pipe 6 contains the solvent,the first portion of the oxirane, the unconsumed peroxide compound andthe unconverted olefin. This medium passes through a filter 7 and isconveyed via pipe 8 into the container 9, in which it undergoes adepressurization. The medium is then conveyed via pipe 10 into adistillation column 11. A mixture of oxirane and of unconverted olefinis recovered at the top of this distillation column 11. This mixture isconveyed via pipe 12 into a condenser 13 which separates the oxiranefrom the unconverted olefin. The unconverted olefin is recycled intoreactor 1 via pipes 14, 3 and 4. The first portion of oxirane iscollected as finished product via pipe 15. A medium containing thesolvent, the peroxide compound not consumed in reactor 1 and possiblysome of the unconverted olefin is collected at the bottom of thedistillation column 11. This medium, a portion of which may optionallybe recycled into the reactor 1 via pipe 30, is transported via pipe 16into a second reactor 17 containing another portion of the catalyst,preferably in the form of a fluid bed 18. The second reactor 17 is fedwith a second portion of the olefin via pipe 19. In the second reactor17, the second portion of the olefin reacts with the unconsumed peroxidecompound obtained from the first reactor in the presence of catalyst 18to form a second portion of the oxirane. The conditions in the secondreactor 17 are preferably such that all of the peroxide compoundobtained from the first reactor is consumed. The medium leaving reactor17 via pipe 20 thus contains the solvent, the second portion of theoxirane and the unconverted olefin. This medium passes through a filter21 and is conveyed via pipe 22 into the container 23, in which itundergoes a depressurization. The medium is then transported via pipe 24into a second distillation column 25. A mixture of the second portion ofoxirane and of unconverted olefin is recovered at the top of thisdistillation column 25. This mixture is conveyed via pipe 26 into acondenser 27 which separates the oxirane from the unconverted olefin.The unconverted olefin is recycled into the reactor 1 via pipes 28, 14,3 and 4. The second portion of oxirane is collected as finished productvia pipe 29. The solvent, which is collected at the bottom of thedistillation column 25, and is recycled via pipe 4 into the firstreactor 1.

[0015] The catalyst used in the process according to the inventiongenerally contains a zeolite as active element, and preferably atitanium zeolite. The term “titanium zeolite” is intended to denote asolid containing silica which has a microporous crystal structure ofzeolite type and in which several silicon atoms are replaced withtitanium atoms. The titanium zeolite advantageously has a crystalstructure of ZSM-5, ZSM-11, ZSM-12, MCM-41 or ZSM-48 type. It may alsohave a crystal structure of beta zeolite type, preferably free ofaluminium. Zeolites with an infrared absorption band at about 950-960cm⁻¹ are suitable for use. Titanium zeolites of silicalite type arepreferred. Those corresponding to the formula xTiO₂(1−x)SiO₂ in which xis from 0.0001 to 0.5 and preferably from 0.001 to 0.05 givehigh-quality performance. Materials of this type, known under the nameTS-1, have a microporous crystalline zeolite structure similar to thatof the zeolite ZSM-5.

[0016] The catalyst used in the process according to the invention isadvantageously in the form of particles obtained by extrusion asdisclosed in patent application WO 99/28029 by the Applicant, or by aspray process as disclosed in patent application WO 99/24164 by theApplicant. The content of these two patent applications is incorporatedherein by reference.

[0017] The solvent used in the process according to the invention may bechosen from linear or branched saturated aliphatic alcohols. Thealcoholic solvent generally contains up to 10 carbon atoms andpreferably from 1 to 6 carbon atoms. Examples which may be mentioned aremethanol and ethanol. Methanol is preferred.

[0018] The amount of solvent used in the first reactor is generally atleast 25% by weight of the liquid reaction medium present in the firstreactor, in particular at least 40% by weight, for example at least 50%by weight. This amount usually does not exceed 99% by weight and inparticular does not exceed 95% by weight.

[0019] The molar ratio between the amounts of olefin and of peroxidecompound that are used in the process according to the invention isgenerally at least 0.1, in particular at least 0.2 and preferably atleast 0.5. This molar ratio is usually not more than 100, in particularnot more than 50 and preferably not more than 25.

[0020] The process according to the invention may be continuous orbatchwise.

[0021] In the process according to the invention, when it is performedcontinuously, the peroxide compound is generally used in the firstreactor in an amount of at least 0.005 mol per hour and per gram ofcatalyst present in the first reactor, in particular at least 0.01 mol.The amount of peroxide compound is usually less than or equal to 25 moland in particular less than or equal to 10 mol. Preference is shown foran amount of peroxide compound of greater than or equal to 0.03 mol andless than or equal to 2.5 mol.

[0022] In the process according to the invention, the peroxide compoundis advantageously used in the form of an aqueous solution. In general,the aqueous solution contains at least 2% by weight of peroxide compoundand in particular at least 5% by weight. It usually contains not morethan 90% by weight of peroxide compound and in particular not more than70% by weight.

[0023] The temperature of the reaction between the olefin and theperoxide compound may range from 10° C. to 125° C. In one advantageousvariant as disclosed in patent application EP 99/08703 by the Applicant,it is greater than 35° C. in order to overcome the gradual deactivationof the catalyst. The temperature may be greater than or equal to 40° C.and preferably greater than or equal to 45° C. A temperature of greaterthan or equal to 50° C. is most particularly preferred. The reactiontemperature is preferably less than 100° C.

[0024] In the process according to the invention, the reaction betweenthe olefin and the peroxide compound may take place at atmosphericpressure. It may also take place under pressure. This pressure generallydoes not exceed 40 bar. A pressure of 20 bar is suitable in practice.

[0025] The peroxide compounds which may be used in the process accordingto the invention are peroxide compounds containing one or more peroxidefunctions (—OOH) which may release active oxygen and which are capableof carrying out an epoxidation. Hydrogen peroxide and peroxide compoundswhich may produce hydrogen peroxide under the conditions of theepoxidation reaction are suitable for use. Hydrogen peroxide ispreferred.

[0026] When hydrogen peroxide is used, it may be advantageous to use, inthe process according to the invention, an aqueous hydrogen peroxidesolution in crude form, i.e. in unpurified form. For example, a solutionobtained by simple extraction, with substantially pure water, of themixture obtained from the oxidation of at least onealkylanthrahydroquinone (process known as “autoxidation AO process”) maybe carried out, without a subsequent washing and/or purificationtreatment. These crude hydrogen peroxide solutions generally containfrom 0.001 to 10 g/l of organic impurities expressed as TOC (TotalOrganic Carbon). They usually contain metal cations (such as alkalimetals or alkaline-earth metals, for instance sodium) and anions (suchas phosphates or nitrates) in contents of from 0.01 to 10 g/l.

[0027] In another variant of the process, a hydrogen peroxide solutionproduced by direct synthesis from oxygen and hydrogen in the presence ofmethanol may be used.

[0028] The oxirane which may be prepared by the process according to theinvention is an organic compound comprising a group corresponding to thegeneral formula:

[0029] The oxirane generally contains from 2 to 10 carbon atoms andpreferably from 3 to 6 carbon atoms. The oxiranes which may be preparedadvantageously by the process according to the invention are1,2-epoxypropane and 1,2-epoxy-3-chloropropane. The preferred oxirane is1,2-epoxypropane.

[0030] The olefins which are suitable for use in the process accordingto the invention generally contain from 2 to 10 carbon atoms andpreferably from 3 to 6 carbon atoms. Propylene, butylene and allylchloride are suitable for use. Propylene and allyl chloride arepreferred. Propylene is most particularly preferred.

[0031] In the process according to the invention, it may prove to beadvantageous to monitor the pH of the liquid phase. For example, it maybe advantageous to maintain the pH of the liquid phase during thereaction between the olefin and the peroxide compound at a value of from4.8 to 6.5, for example by adding a base (sodium hydroxide) to theepoxidation medium, as recommended in patent application WO 99/48882 bythe Applicant (the content of which is incorporated into the presentpatent application by reference). This base may be introduced into onlyone reactor (for example the first reactor) or into several reactors. Itis preferably introduced into each reactor.

[0032] The reaction between the olefin and the peroxide compound may becarried out in the presence of a salt such as sodium chloride, asdisclosed in patent application WO EP 99/08703 by the Applicant (thecontent of which is incorporated by reference into the present patentapplication). This salt may be introduced into only one reactor (forexample the first reactor) or into several reactors. It is preferablyintroduced into each reactor.

[0033] It may be advantageous to introduce the olefin in a form dilutedin one or more alkanes. For example, a fluid containing the olefin andalso at least 10% (in particular 20%, for example at least 30%) byvolume of one or more alkanes may be introduced into the epoxidationreactors. For example, in the case of propylene, the latter may be mixedwith at least 10% by volume of propane when the recycled unconvertedpropylene is introduced into the reactor. It may also be a source ofpropylene which is not completely freed of propane.

1. Process for manufacturing oxirane by reaction of an olefin with aperoxide compound in the presence of a catalyst and a solvent in atleast two reactors arranged in series, each of which contains a portionof catalyst, according to which a first portion of the olefin, thesolvent and all of the peroxide compound are introduced into a firstreactor, an epoxidation of the first portion of the olefin is carriedout therein in order to form a first portion of the oxirane, a mediumcomprising the first portion of the oxirane formed, the solvent, theunconsumed peroxide compound and possibly the unconverted olefin isremoved from this reactor, the medium and another portion of the olefinare introduced into a subsequent reactor, an epoxidation of the otherportion of the olefin is carried out therein using the unconsumedperoxide compound obtained from the first reactor, in order to formanother portion of the oxirane, and the other portion of the oxiranethus formed is collected.
 2. Process according to claim 1, in which 50%to 99% of the total amount of peroxide compound used in the firstreactor is consumed in the first reactor, the remainder being consumedin the subsequent reactor(s).
 3. Process according to claim 1 or 2, inwhich all the reactors are of identical size.
 4. Process according toany one of claims 1 to 3, in which the catalyst is present in eachreactor in the form of particles, at least some of which are influidized form.
 5. Process according to claim 4, in which the mediumleaving the first reactor passes through a filter before beingintroduced into the subsequent reactor.
 6. Process according to any oneof claims 1 to 5, in which the medium entering the subsequent reactor isfirst subjected to a depressurization before being introduced into thesubsequent reactor.
 7. Process according to any one of claims 1 to 6, inwhich the medium entering the subsequent reactor is first subjected to atreatment to separate out the oxirane formed before being introducedinto the subsequent reactor.
 8. Process according to claim 7, in whichthe separation treatment is a distillation.
 9. Process according to anyone of claims 1 to 8, in which the oxirane is epichlorohydrin, theolefin is allyl chloride, the peroxide compound is hydrogen peroxide,the solvent is methanol and the catalyst contains TS-1.
 10. Processaccording to any one of claims 1 to 8, in which the oxirane is propyleneoxide, the olefin is propylene, the peroxide compound is hydrogenperoxide, the solvent is methanol and the catalyst contains TS-1.